I recently fully serviced this Seiko 6139-7010 Speed-Timer Chronograph for a ClockSavant customer. This particular watch is one of the first Seiko automatic chronograph’s manufactured. The 6139 was introduced in 1969 and this watch was manufactured in March of 1970.As you can see from the “before” pictures, many years ago the watch was badly damaged by someone pouring an acid-like liquid into the watch that both ate-away at some steel and caused corrosion at the same time— someone’s idea of a miracle liquid to get a watch running again.It was quite a brawl between me and the wear and damage to this watch but the results are quite pleasing, this is really a stunning watch that speaks to its past, beauty, and perseverance. It’s now highly accurate and I was successful at achieving a good level of water resistance despite the case corrosion I needed to address.Servicing a mechanical chronograph properly by fully and completely disassembling them is already difficult. I’ve discussed in previous posts how the “servicing” collectors often purchase is shortcut that doesn’t involve a full disassembly. And once fully disassembled, the work starts, not stops, there. Returning to this watch, I wanted to add a few more comments on the different 6139 versions. There were two calibre 6139 versions, 6139A and 6139B. This watch houses the first version, 6139A. A and B are different in several aspects. While I wouldn’t describe one version as better than the other, the A version does include an additional escape wheel cap jewel on the dial side which is not particularly useful as it’s only on one side of the train, and I prefer the chronographs hammer/spring design over the B, though both are fine. I like the red lettering on the automatic module in the A version.